1. Field of the Invention
The present invention relates to techniques for identifying a computer system. More specifically, the present invention relates to a method and apparatus for generating an EMI fingerprint for a computer system.
2. Related Art
A given semiconductor chip design can be implemented in a number of different versions of the chip. For example, the different versions can include chips with varying speeds and chips with incremental changes to the functionality. Hence, it is often useful to be able to identify the specific version of a semiconductor chip.
One technique for identifying a semiconductor chip involves reading the serial number printed on the package for the chip. Unfortunately, if the semiconductor chip is integrated within a computer system, this is time-consuming and burdensome because the computer system must be opened to perform a visual inspection of the chip. Furthermore, this process may additionally involve identifying one of many system boards within a server containing the semiconductor chip, and pulling the system board from the server. One solution to this problem is to include an identifier within the semiconductor chip which can be read by an operating system. Unfortunately, some semiconductor chips do not include identifiers which can be read by an operating system. Furthermore, some operating systems may not provide a mechanism for reading an identifier from a semiconductor chip.
It is important to be able to correctly identify semiconductor chips within a computer system if the computer system is to be exported. For example, a government may restrict the computational power of computer systems which can be exported to specified countries. However, an unscrupulous vendor may modify a computer system that does not violate the export control restriction by substituting a more powerful central processing unit (CPU) into the computer system, and may then attempt to ship the modified computer system to an export-controlled country. Border inspectors who visually inspect the model number of the computer system may not be able to determine that the computer system has been modified. Furthermore, the vendor may modify the operating system so that the identifier for the substituted semiconductor chip is identified as a less-powerful chip. Hence, booting up the computer system in order to determine the CPU identifier embedded within the CPU is not necessarily a reliable technique.
Another problem is the possibility that a CPU within the computer system may be substituted with a spy chip, or a piggy-back semiconductor chip may be coupled to the CPU to obtain information from the computer system. Unfortunately, it is difficult to detect this type of tampering. A system administrator must open the computer system and visually inspect the components within the computer system to determine whether the computer system has been tampered with. In the case where a spy chip is substituted for the CPU chip, a visual inspection may not suffice if the serial number of the chip and the identifier within the chip have been set to match the serial number and identifier for the original CPU.
Hence, what is needed is a method and an apparatus for identifying a semiconductor chip without the problems described above.